A crossbow is designed to fire a bolt at velocities significantly larger than those achievable using a so-called vertical bow. The greater energy storage in the limbs of the crossbow requires larger draw weights; drawing the crossbow against those larger draw weights usually requires some sort of draw mechanism to assist the user (i.e., an arbalist or crossbowman) to draw the crossbow. Over the centuries many different techniques, devices, and arrangements have been devised for drawing a crossbow. Examples include, but are not limited to, hand-spanning, belt hook, rope and pulley, pushing or pulling levers, latchet, windlass or winch, lead screw, or cranequin.
One of many examples of a crossbow drawn by a winch mechanism is disclosed in U.S. non-provisional application Ser. No. 15/784,138 filed Oct. 15, 2017, which is incorporated by reference as if fully set forth herein. An example of such a crossbow 10 is shown in FIGS. 5 and 6 in undrawn (brace) and drawn arrangements, respectively, and includes a stock 20, an elongated mainframe 12, bow limbs 30, a bowstring 50, stationary and reciprocating trigger subassemblies 200 and 300 (respectively), and the winch mechanism 400. A crossbow crank includes a handle 420, a shaft 440, and an arm 450. The crank is attached to the winch mechanism 400 and used to operate the winch mechanism 400 to draw the crossbow 10 to its drawn arrangement (e.g., as in FIG. 6) and, in some instances, to allow the crossbow 10 to return to its undrawn, brace arrangement (e.g., as in FIG. 5) in a controlled manner without firing the crossbow 10. Operating the winch mechanism 400 to draw the crossbow 10 causes a rope 16 to be taken up by a spool of the winch mechanism 400, which in turn pulls the reciprocating trigger subassembly 200 (and the bowstring 50 held by it) rearward along a mainframe 12 of the crossbow 10. The winch mechanism 400 includes a clutch that, when it is engaged, only permits the winch mechanism 400 to take up the rope 16; the clutch does not permit the rope 16 to be let out unless the clutch is disengaged. In the drawn arrangement, the reciprocating trigger subassembly 200 and the stationary trigger subassembly 300 are relatively positioned to allow the crossbow 10 to be triggered and a bolt to be launched from it. Further details of the arrangement of the example crossbow 10 are not pertinent to the present disclosure, and are not elaborated upon herein. The crank typically can be detached from and reattached to the winch mechanism 400, so that it can be moved out of the way when not in use (e.g., after drawing the crossbow and while aiming and firing it).
The mechanical advantage provided by the winch mechanism 400 and the crank enable the user to draw the crossbow 10 against the large draw force. The clutch, when engaged, typically prevents the tension in the bowstring 50 from pulling forward the reciprocating trigger subassembly 200. After firing the crossbow 10, the clutch is disengaged by the user to allow the reciprocating trigger subassembly 200 to be moved forward to prepare for the next shot. The mechanical advantage also enables the user to let the crossbow 10 return to its brace arrangement in a controlled manner (without being fired; also referred to as decocking the crossbow 10), by resisting the force exerted by the bowstring 50. Such decocking requires disengagement of the clutch.
The mechanical advantage described above, that permits use of the crossbow 10 despite the large draw force, also can result in the winch mechanism 400 and crank (if not properly controlled by the user) being spun very rapidly in response to the force exerted by the bowstring 50. For example, if the clutch is erroneously disengaged during or after drawing the crossbow 10, while the user is not holding the crank handle 420, there is nothing to prevent the tension on the bowstring 50 from pulling the reciprocating trigger subassembly 200 forward, pulling the rope 16 off of the spool of the winch mechanism 400, and causing the winch mechanism 400 and the crank handle to spin. In another example, if the user's hand should slip off of the crank handle 420 during decocking of the crossbow 10 (while the clutch is disengaged), a similar uncontrolled spin can occur. During such uncontrolled spins, the energy stored in the deformed bow limbs 30, which during a normal shot would be transferred to the launched bolt as translational kinetic energy, is instead at least partly transferred to the winch mechanism 400 and the crank as rotational kinetic energy. The uncontrolled spinning can cause damage to the crossbow 10; a potential might exist for injury to the user as well, particularly his hand or fingers. If the spinning causes the crank to detach and fly off, other damage or injuries potentially could result.